1. Field of the Invention
The present invention relates to a network camera which transmits image data in real time to a server connected thereto via a network such as the Internet.
This application claims priority of Japanese Patent Application No. 2003-188464, filed in Japan on Jun. 30, 2003, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
In recent years, broadband environment such as an ADSL (Asymmetric Digital Subscriber Line) has become widespread, and a network camera has accordingly come into use, which allows, for example, viewing of the images that are transmitted, through the Internet, from the remotely located network camera on the screen of a personal computer or mobile phone, or viewing of the images transferred from the network camera located within a LAN (Local Area Network) installed in a factory or company on the screen of the personal computer. An image pickup screen of the network camera can be moved by remote control such as pan/tilt operation, allowing wide-area viewing.
Some of the above network camera applications are set as an FTP (File Transfer Protocol) client to upload image data to an FTP server installed on a network.
FTP is defined in RFC (Requests For Comment) 959 published by IETF (Internet Engineering Task Force), which is a consortium established for the purpose of advancing standardization of new technologies available on the Internet. FTP is a protocol (or command that implements the FTP protocol) for file transfer between a client and a host computer on a TCP/IP (Transmission Control Protocol/Internet Protocol) network such as the Internet or intranet, and has been used on the Internet as frequently as an HTTP (HyperText Transfer Protocol) or an SMTP (Simple Mail Transfer Protocol)/POP (Post Office Protocol).
There is a possibility that a network for data transfer is temporarily out of service for many reasons. It is known that ADSL transmission, which has become increasingly widespread in recent years, is weak against electromagnetic noise, and accordingly, a line fault frequently occurs depending on the installation environment. Further, a network is constructed and managed by various kinds of equipments, and there is also a case where a network line is out of service due to maintenance of these equipments. When the network breakdown occurs in a conventional FTP client/server system, the image data being transferred during this breakdown time is treated as send error, with the result that the image data will not be transmitted to the FTP server. A loss of the required image data is a serious problem in a security monitoring system, which poses a major obstruction to an introduction of the network camera to a security system.